1. Field of the Invention
This invention relates to an air-drying unsaturated alcohol-modified polyester which, by virtue of its low viscosity, may be made up into solvent-free or at least substantially solvent-free lacquer binders.
2. Statement of the Related Art
Lacquers are normally applied by spray coating, spread coating or dip coating. In this connection, it is important that their viscosity should not exceed a certain maximum to guarantee good levelling and complete wetting. Normally, the viscosity is adjusted by the addition of solvents or diluents. However, solvents and diluents are troublesome during processing and pollute the environment by evaporation, so that there have been several attempts to restrict their use at least in quantitative terms. In the field of oven-drying in lacquers, it is proposed in U.S. Pat. No. 4,031,047 and corresponding German published patent application No. 25 05 246 to replace part of the solvent by a constituent capable of polymeric condensation, namely caprolactam. U.S. Pat. No. 4,049,599 proposes for oven-drying lacquers a low viscosity, relatively low molecular weight polyester based on fatty acids, polyols and polybasic carboxylic acids.
However, it has not yet been possible to apply the two solutions mentioned above to air-drying systems. The air drying of alkyd resins is a comparatively slow crosslinking reaction which leads more quickly to hard coatings, the higher the starting molecular weight of the resin. However, the viscosity of the resin solutions and, therefore, the quantity of solvent/diluent required to obtain processible preparations increases with increasing molecular weight.